R.F Zhang

Thick hydroxyapatite coatings by electrophoretic deposition

Abstract Submicron hydroxyapatite (HA) powders prepared by thermal plasma spray method were electrophoretically deposited on carbon rod by repeated depositions at room temperature. The thickness of green coating was adjusted by deposition time and the number of depositions. After sintering, a uniform HA ceramic tube was obtained. A range of sintering temperature from 1150 to 1300 °C was studied. From the Fourier transform-infrared (FT-IR) spectra and SEM results, the sintering temperature has shown an obvious influence on the microstructure and densification, hence the strength of the sintered coatings. No HA decomposition was observed up to 1300 °C of sintering by X-ray diffraction (XRD) analysis. The influence of processing factors such as electrophoretic mobility of particles, suspension concentration, applied electric field and deposition time on coating behavior was also discussed.

Barium titanate derived from mechanochemically activated powders

Abstract A high-energy ball milling process was applied to a mixture with equal molar ratio of BaCO 3 and TiO 2 . X-ray diffraction data indicated that there was no reaction happening during the milling process although the particle size was greatly reduced. The effect of post-annealing on the phase formation and grain growth of BaTiO 3 was investigated by thermal analysis (DTA/TGA), X-ray diffraction (XRD) and scanning electron microscopy (SEM). No reaction was observed in the sample annealed at 600°C. Ba 2 TiO 4 was found as the mixture annealed at 700°C. An 800°C-annealing led to single phase BaTiO 3 with a cubic structure. The temperature at which BaTiO 3 phase was derived is lower than required by the solid-state reaction process, which could be attributed to the refined grains/particles of the mixture as a result of high-energy ball milling. Tetragonal structured BaTiO 3 was formed at 1150°C together with a sharp increase in grain size.

Effect of transition metal oxides on mullite whisker formation from mechanochemically activated powders

The effect of transition metal oxides, including FeO1.5, CoO and NiO, on the phase formation and morphology development of mullite (3Al2O3·2SiO2) whiskers from oxide mixtures activated by the high-energy ball milling process, were investigated. With the addition of FeO1.5, the mullite formation temperature was almost the same as that required for the system of Al2O3 and SiO2 without doping, while the presence of CoO and NiO inhibited the mullitization. The effect of the transition metal oxides on the mullite phase formation could be explained in terms of the mullitization mechanism. The size of the whiskers in the CoO-doped samples was larger than that in the samples doped with FeO1.5 and NiO. The present result showed that the dimension of the whiskers could be altered through addition transition metal oxides.

PZT-based materials with bilayered structure: preparation and ferroelectric properties

Abstract In the present work, bilayered PZT-based ceramic materials were successfully produced via dry pressing and sintering. The densification, compositional phase, and microstructure of the materials prepared were investigated. Ferroelectric properties of the materials were measured and the relationship between property and layer volume composition was discussed. The present work reported a simply method to fabricate ferroelectric materials incorporating good parameters, such as higher remanent polarization, dielectric constant, and lower dielectric loss, which meet the material demand of both higher performance and longer service time.

Colloidal characterization and electrophoretic deposition of PZT

It is widely accepted that colloidal stability has a great effect on the quality of the products in wet processing of ceramics such as electrophoretic deposition. In this work, colloidal stability of submicron PZT powders in ethanol was studied. Zeta potential and viscosity of PZT powder suspension as a function of pH were measured. Electrosteric effect resulted from the addition of PVA polymer to the suspension was also investigated. The dispersing quality of the polymeric solvent was quantified by viscosity measurement and represented by a solvent quality parameter. The effect of polymer addition to the PZT suspension on zeta potential was also determined as a function of pH. The electrostatic effect was also discussed using the DLVO theory. Lastly, electrophoretic deposition (EPD) was carried out using the identified optimum suspension conditions.

Mullite phase formation and reaction sequences with the presence of pentoxides

Abstract The effects of pentavalent oxide (M2O5, M=V, Nb and Ta) on the phase formation of mullite, reaction sequence and microstructure development in the oxide mixtures have been investigated. It was found that V2O5 accelerated the mullite phase formation while Nb2O5 and Ta2O5 inhibited the mullitization. No reaction was observed between V2O5 and Al2O3 or SiO2, while a complicated reaction sequence was found in the mixtures doped with Nb2O5 and Ta2O5. V2O5 doping resulted in anisotropic grain growth, while equiaxed grains were grown from samples doped with Nb2O5 and Ta2O5. The three groups also demonstrated a different densification behavior. Samples doped with V2O5 were of a much lower density than the theoretical density of mullite, due to the anisotropic grain growth. The densification of the Nb2O5 and Ta2O5 groups was similar to the mixture of Al2O3 and SiO2 without dopants. These differences could be explained in terms of the role that the pentavalent oxides played during the formation of the SiO2-rich liquid phase in the mixtures.

Lead zirconate titanate ceramics achieved by reaction sintering of PbO and high-energy ball milled (ZrTi)O2 nanosized powders

Abstract Lead zirconate titanate [Pb(Zr x Ti 1− x )O 3 or PZT, x =0.40, 0.48, 0.52 and 0.56] ceramics were prepared via a one-step reaction sintering of PbO and (Zr x Ti 1− x )O 2 powders at a temperature lower than that required in the conventional process. The (Zr x Ti 1− x )O 2 powders with nanometer grain size were synthesized by a high-energy ball milling process at room temperature. The final PZT mixture systems demonstrate a reaction temperature of 720–750 °C and a maximum sintering rate temperature of 800–830 °C, both of which are much lower than that observed from the conventional solid-state reaction process for PZT ceramics. In the present work, the 1100 °C-sintered Pb(Zr 0.52 Ti 0.48 )O 3 ceramics formed possess a dielectric constant of 1126, a remnant polarization of 22 μC/cm 2 and a coercive field of 12.6 kV/cm. These values are in good agreement with that widely reported for PZT ceramics. The results hence indicate that the sintering reaction process in the present work is practical for PZT processing and may be applicable to other Pb containing multi-component ceramic materials.

PZT ceramics derived from hybrid method of sol-gel and solid-state reaction

Abstract Lead zirconate titanate [Pb(Zr 0.52 Ti 0.48 )O 3 , PZT] ceramics were prepared by a hybrid method of sol-gel and solid-state reaction. Reaction of the oxides to PZT occured at a temperature as low as 500 °C, which is believed to be induced by the PZT crystallized from the sol-gel portion in the system. Fully dense PZT ceramics with 99% of the theoretic density have been achieved from the partially reacted mixture at a sintering temperature of 1100 °C for 1 h. The good dielectric ( K =1030, δ =3%) and ferroelectric ( P r =24.3 μC/cm 2 , E c =12 kV/cm) properties of the sintered PZT ceramic measured in the present work are in good agreement with the widely reported results of other processing techniques in the literature, indicating the practicality of the hybrid method for the preparation of PZT ceramics. It is also believed to be applicable to other materials that can be processed via sol-gel technique.

Fabrication and characterization of lead lanthanum zirconate titanate (PLZT7/60/40) ceramics from oxides

Lead lanthanum zirconate titanate (PLZT7/60/40) ceramics were fabricated from their oxide mixture via a direct sintering process without involving the calcination step. Different levels of excess PbO (0, 10 and 20 mol%) were used to check its effect on microstructure and thus the electrical properties of the PLZT ceramics. The reaction and densification behavior of the oxide mixtures for the PLZT ceramics were monitored by using a dilatometer. The electrical properties of the PLZT ceramics and their relationships with the processing parameters and excess PbO levels were characterized and discussed.

Fabrication and characterization of bilayered Pb(Zr,Ti)O3-based ceramics

A bilayered lead zirconate titanate (PZT)-based ceramic was successfully fabricated by a simple dry pressing and free sintering process. The phase, density, microstructure, and ferroelectric properties of the material prepared were investigated. The present work reported a feasible production method to achieve a ceramic combining good parameters for both higher performance and longer service time.